The invention relates to a presetting device for a tool holder which holds the shank of a rotary tool, in particular of a milling or drilling tool, in an interference fit in a locating opening and releases said shank during heating, in particular by means of an induction heating arrangement.
It is known from WO 01/89758 A1 to hold rotary tools, such as, for example, milling cutters or drills, in a central locating opening of a tool holder exclusively by an interference fit of a sleeve part, forming the locating opening, of the tool holder. The sleeve part of the tool holder, by means of an induction heating arrangement, for example in the form an alternating-current-fed induction coil enclosing the sleeve part, can be heated to such an extent that the shank of the rotary tool can be inserted into the locating opening or removed from it again. The outside diameter of the shank is slightly larger than the nominal inside diameter of the locating opening, so that, when the sleeve part has cooled down, the latter holds the shank in an interference fit.
Conventional tool holders of the above type have a standard coupling, for example a steep-angle-taper coupling or an HSK coupling, by means of which the tool holder is coupled to the spindle of the production machine. In this case, a reference stop surface permits reproducible measuring of the axial position of the rotary tool relative to the spindle or to the tool holder by means of a conventional length-measuring device measuring the distance between a reference stop surface of the spindle or the tool holder and the tip of the rotary tool and thus permits reproducible axial positioning of the tool holder relative to the spindle.
Furthermore, it is known to arrange an axially adjustable positioning stop surface for the tool shank in the locating opening of shrink-fit tool holders of the type explained above. Such a positioning stop surface can be realized, for example, by a screw which projects axially into the locating opening and limits the plunge-in depth of the tool shank in an adjustable manner during the shrink fitting.
Although machine tools permit the subsequent adaptation of the machine setting to the length of the tool-holder/rotary-tool unit, it has nonetheless proved to be advantageous if the rotary tool can be shrunk in a defined axial position relative to the tool holder, in particular a reference stop surface of the tool holder, by presetting the positioning stop surface of the tool holder. Since the period during which these elements are heated is kept as short as possible in order to avoid thermal damage to the tool holder or to the rotary tool, it is desirable for the tool holder not to be adjusted during its heating phase but for it to be adjusted before the shrink-fit operation in such a way that it holds the rotary tool in a predetermined position after the shrink fitting. In addition, the presetting of the positioning stop surface is more accurate when the tool holder is still cold, since no thermal expansions of the tool holder affect the measuring result.
It is the object of the invention to provide a device by means of which axially adjustable shrink-fit tool holders can be preset in the cold state quickly and precisely in such a way that the unit of tool holder and rotary tool has a predetermined axial length after the shrink-fit operation.
In the solution achieving this object, the invention is based on a presetting device for a tool holder which holds the shank of a rotary tool, in particular of a milling or drilling tool, in an interference fit in a locating opening and releases said shank during heating, in particular by means of an induction heating arrangement, and which has inside the locating opening an axially adjustable positioning stop surface for the tool shank. The improvement according to the invention is characterized by the following features:
a) a holder receptacle which holds the tool holder in an axial position and defines an axial opposing reference surface,
b) means for measuring the axial overall length of the rotary tool, and
c) a measuring device which measures the axial distance between the positioning stop surface of the tool holder and the opposing reference surface of the holder receptacle and has a measured-value indicator, the indicated distance value of which can be increased by the measured value of the overall length of the rotary tool.
Such a presetting device, at its measured-value indicator, directly indicates the value of interest in practice between the tip of the rotary tool and a predetermined reproducible position in a holder receptacle. During the presetting measurement, the tool holder sits in a holder receptacle of the presetting device in a manner compatible with practice, and it is sufficient for the length adjustment if the positioning stop surface is adjusted while its distance from the opposing reference surface of the holder receptacle is measured. The presetting device may be separate from the shrink-fitting apparatus inductively heating the tool holder, but preferably forms a construction unit with the shrink-fitting apparatus, in particular when the shrink-fitting apparatus comprises a rotary table on which the tool holder sitting in the holder receptacle is transported successively through a presetting station, in which it is adjusted for the predetermined length, a shrink-fitting station, in which the rotary tool is inserted, and if need be a cooling station, in which the tool holder with rotary tool shrunk in place is cooled again to room temperature.
In a preferred configuration which can be composed of commercially available length-measuring components, provision is made for the measuring device to have a first electric position transducer, which delivers a first distance signal representing the distance between the positioning stop surface and the opposing reference surface, for the means for measuring the overall length of the rotary tool to comprise a second electric position transducer, which delivers a second distance signal representing the overall length, and for the measured-value indicator to comprise means for the summation of the first and the second distance signal and for it to indicate a value representing the sum of the distance signals. The position transducers are preferably digital position transducers, which do not even have to contain measured-value memories, since the rotary tool can remain in the measuring position of the second position transducer during the axial adjustment of the tool holder.
In a variant of the presetting device, a single electrical or mechanical length-measuring instrument is sufficient if the measuring device has two measuring probes which are guided in a displaceable manner in the axial direction of the tool holder relative to the opposing reference surface and of which a first measuring probe is intended for bearing with a measuring surface against the position stop surface of the tool holder, and the second measuring probe is intended for bearing with a measuring surface against an axial end of the rotary tool, while the rotary tool, parallel to the axial direction of the tool holder, bears with its other axial end either on a reference surface of the first measuring probe or on the opposing reference surface, the measuring device measuring the distance between the measuring surfaces of the two measuring probes, and it being possible for the measured-value indicator to be set to zero value indication when the first measuring probe bears on the opposing reference surface and the second measuring probe bears on the reference surface of the first measuring probe or on the rotary tool, respectively. A presetting device of this type, which can in turn be combined with the shrink-fitting apparatus to form a construction unit, provides for a mechanical sum operation, so that here, too, the measured-value indication indicates the sum value of interest in practice.
In order to simplify the manipulation, the first measuring probe and the second measuring probe are expediently guided in a displaceable manner independently of one another on a stationary guide column perpendicular to the opposing reference surface, the reference surface on which the rotary tool is to be put for the presetting operation being expediently arranged on the top side of the first measuring probe in the displacement path of the second measuring probe.
Alternatively, the first measuring probe may be guided on a stationary guide column perpendicular to the opposing reference surface, the second measuring probe then being guided on the first measuring probe in a displaceable manner parallel to the displacement direction of the latter, and the opposing reference surface lying in the displacement path of the second measuring probe. In this variant, the rotary tool, for determining its length, is put on the opposing reference surface, a factor which reduces the overall height of the presetting device compared with the first-mentioned variant. In both variants, however, commercially available length-measuring instruments may be used.
Although the presetting of the tool holder could also be carried out with the axis of the tool holder arranged in a horizontal position, the tool receptacle is nonetheless preferably arranged in such a way that it accommodates the tool holder with the locating opening open at the top, since this facilitates the manipulation, in particular if the tool receptacle is already an integral part of the shrink-fitting apparatus. The measuring device expediently has an elongated measuring-probe extension which can be inserted into the locating opening from the tool-insertion side of the tool holder into the latter right up to the positioning stop surface and which is preferably in the form of a continuously open sleeve which permits the insertion of an adjusting tool for the position adjustment of a positioning element, forming the positioning stop surface, for example of a positioning screw of the tool holder. In this way, the measuring operation and the adjusting operation can be carried out from above. The adjusting tool may be separate from the measuring-probe extension. However, it may also form a unit with the measuring-probe extension, provided the measuring-probe extension is mounted on the measuring device in a rotatable manner, that is to say it is at the same time used as an adjusting tool.
In conventional rotary tools, the end face of the shank usually does not run exactly at right angles to its rotation axis. If such a rotary tool is put on a reference surface in order to measure its overall length, this leads to an incorrect measurement with regard to the position of the shank with respect to the positioning stop surface of the tool holder. In a preferred configuration of the presetting device, in which the overall length of the rotary tool is measured by means of a measuring device, provision is made for the shank of the rotary tool, during the measurement of the overall length, to be axially supported with its end face on a supporting holder, which supports the end face at a reference stop surface of a supporting projection, at which the diameter of this reference surface is smaller than the shank diameter. The diameter of the reference stop surface of the supporting projection is preferably approximately equal to the diameter of the positioning stop surface of the tool holder. The supporting projection, during the measurement of the overall length of the rotary tool, thus xe2x80x9csimulatesxe2x80x9d the positioning stop surface, usually formed by an adjusting screw, of the tool holder. A supporting holder of the aforesaid type may also be used in presetting devices other than those explained above and thus has independent inventive significance.
The supporting holder also expediently has supporting surfaces which radially support the shank of the rotary tool at its circumference and which are in particular in the form of prismatic surfaces which center the shank. Spring-loaded pressure means are preferably assigned to the prismatic surfaces, which means clamp the shank between the prismatic surfaces.
In order to simplify the measurement of the overall length, the supporting holder, at a distance from the reference stop surface of the supporting projection, has a reference surface which is parallel to and, in particular, in alignment with the reference stop surface and is accessible for the measurement and which permits the zero setting of the measuring device with regard to the reference stop surface of the supporting projection.
The supporting holder expediently comprises several groups of supporting surfaces, in particular prismatic surfaces, in order thus to be able to measure rotary tools having shanks of differing thickness.